The present invention relates to a process for synthesis of a porphyrin compound using a molecular sieve catalyst under microwave radiation. More particularly, the present invention relates to a process for synthesis of tetraaryl porphyrin by reacting pyrrole and aromatic aldehyde under microwave irradiation, which is a solvent free system using a specific zeolite catalyst. The invention also relates to a process for the synthesis of tetraphenyl porphyrin by reacting pyrrole with benzaldehyde in presence of zeolite molecular sieves under microwave irradiation. The present invention relates to synthesis of porphyrin compounds over solid acid catalyst.
This invention provides a non-corrosive, eco-friendly process, where the catalyst can be recyclable and reuse for many times, no work up procedure, no-wastage of the compounds (i.e. high atom selectivity), simple sample extraction and high selectivity of products.
Porphyrin compounds as well as methods for synthesising the same are well recognised in the art. However, porphyrin compounds and other pyrrole compounds are expensive. For example porphyrine is offered at costs as high as $15,000/g. Even though many catalysts such as organic and inorganic acid catalysts are known for the synthesis of porphyrins, the catalysts have at best limited facility for reuse and the yields are very low. Another disadvantage of the prior art processes for the synthesis of porphyrins using such catalysts is that impure corroles are formed making it difficult to separate the pure compound.
The first such report of synthesis of porphyrin molecules under microwave irradiation by A. Petit et al (Synthetic Communication 22 (8) (1992) 1139) employed silica alumina, clay and montmorillonite as a catalyst. However, the results were very poor and not more than 10%.
It is therefore important to develop a process for the synthesis of porphyrins with good yield and where catalyst is reusable thereby resulting in economy of costs.
Zeolite catalysts are known in the art for several processes. Zeolites of ZSM series are available from Conteka, Swedan. Methods for producing them are described in detail in U.S. Pat. No. 3,702,886 (ZSM-5). C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) describe the synthesis of MCM-41 by an aqueous solution of aluminum isopropoxide. An aqueous solution of sodium hydroxide (0.3 g) was added to aluminum isopropoxide (0.38 g) in 50 ml beaker and stirred in hot conditions, till a clear solution was formed. Then 9.4 ml of tetraethyl ammonium hydroxide (TEAOH) and Ludox colloidal silica (9.26 g) were added drop wise while stirring at room temperature. Then hexadecyl tri-methylammonium bromide (10.55 g) was added slowly to the above solution. The pH of the mixture was maintained at 11.0-11.5. Finally, the gel mixture was transferred into an autoclave and heated at 100xc2x0 C. for 24 h. The solid product was recovered by filtration, washed with deionized water and dried in air. All the as-synthesized samples were calcined at 773 K in air.
The main object of the present invention is to provide a selective, solvent free, eco-friendly, economical process for synthesis of tetraaryl porphyrines.
This and other objects of the invention have been achieved by using a zeolite molecular sieve as the catalyst for the microwave radiation method for the synthesis of porphyrins.
Accordingly the present invention provides a process for the synthesis of a tetraaryl porphyrin of the formula 1
said process comprising reacting the corresponding pyrrole and aldehyde in a solvent free system under microwave radiation in the presence of a zeolite molecular sieve catalyst to obtain the compound of formula 1.
In one embodiment of the invention, the zeolite molecular sieve catalyst used is in alkali ion form, ammonium ion form or proton form.
In a further embodiment of the invention, the alkali ion is selected from sodium and postassium.
In another embodiment of the invention, the zeolite molecular sieve catalyst is selected from the group consisting of MCM-41, Al-MCM-41, HY, SAPO-5, ZSM 5 and HZSM-5 (30).
In another embodiment of the invention, the aromatic aldehyde is of the general formula RPhCHO wherein R in the ortho, meta and para positions is selected from the group consisting of methoxy, N, N, dimethyl, hydroxy and nitro.
In a further embodiment of the invention, the aromatic aldehyde used is selected from the group consisting of benzaldehyde, o/m/p-methoxy benzaldehyde, o/m/p-methyl benzaldehyde, o/m/p-nitro benzaldehyde, m/p-hydroxy benzaldehyde, N,N, dimethyl benzaldehyde, 3,4,5 tri methoxy benzaldehyde.
In a further embodiment of the invention, the pyrrole to aldehyde molar ratio is in the range of 1:1 to 1:4.
In yet another embodiment of the invention, the catalyst is regenerated by burning out the carbon deposited thereon by passing air through the catalyst layer at a temperature in the range of 450xc2x0 C. to 550xc2x0 C.
In another embodiment of the invention, the yield of the compound of formula 1 is 23.5%.